Very basic extension that exports all sender of mails in one folder into a CSV, which includes their fullname and email. The extension adds an option to the folder view context menu. Please select the folder to export before starting the export.

Highlight multiple emails, right-click, then select "One-by-One Forward". This extension will allow you to forward the selected emails, one-by-one, to the recipients you specify using your choice of attachment handling.

Create Jira Tickets directly from within Mozilla Thunderbird (based on E-Mails). This Addons saves your Username and Password in clear text. Use on your own risk. (Also, you might need to disable the CSRF Filter in your JIRA Instance.)

SyncKolab can synchronize your calendar, address book and tasks against an IMAP server in Kolab formats version 1 (vCard/iCal) or version 2 (XML) or turn your Thunderbird/Lightning into a native Kolab Client (http://kolab.org).